Telephone accessory devices such as automatic dialers, answering machines, cordless telephones, amplifiers for the audio impaired, etc. have recently become a rapidly growing segment of the consumer electronics market. Telephone answering machines have been in the vanguard of this expanding market and in fact, a telephone call today, made to the largest corporation or to a friend down the street, is likely to be answered by an intelligent machine which requests the caller to leave a message in anticipation of a return call at a later time.
The reasons for this rapid increase in a specialized segment of the consumer electronics market are two fold. First, recent decisions by the various federal agencies governing the telephone industry have removed many restrictions on the "terminal equipment" segment of the telephone industry and permitted any manufacturer to produce a product for connection to the telephone switched network. Second, the cost of electronic equipment has rapidly decreased in recent years, due to the shrinking cost of electronics components and large scale integration. Accordingly, large segments of the population can now readily afford the luxury of automatic dialers, cordless telephones and the joy of composing and broadcasting personalized messages via a telephone answering machine to all those who happen to telephone when the called party is not at home or otherwise indisposed.
Although telephone accessory devices are widely used a problem arises when such devices are used in a multi-line telephone environment and in particular when used with a key telephone system. With a key telephone system a plurality of incoming lines (typically 5) are terminated in a particular office or home and each user can select a particular line by simply pressing the appropriate button on the key telephone and lifting the receiver (going off hook). Going off hook with a key telephone lights a lamp on the telephone which indicates to all other users that a particular line is in use (lamp control) and also causes the telephone in use to stop ringing when an incoming call is received (ringing control). The telephone lines not in use of course ring normally in response to an incoming call. Lamp control and ringing control are provided by appropriate signals being returned to the telephone system to indicate that a particular line is in use. This ability is also known in the telephone industry as an A and A1 closure capability.
The problem with a telephone accessory device, such as an answering machine, is that the vast majority of telephone accessory devices (estimated at 95%) do not have the ability to provide an A and A1 closure signal to the telephone system. Therefore when such an accessory device is in use the appropriate lamp on the remaining telephones in the system does not light and the telephone in use will continue to ring although being in the "off-hook" condition. This of course may result in inadvertent eavesdropping, substantial annoyance to the key telephone user and possible malfunction of the telephone accessory equipment.
It is therefore an object of the instant invention to provide lamp and ringing control for a telephone accessory device when used in a multi-line telephone environment.
The various telephone operating companies are aware of this particular problem and have attempted to provide additional equipment to aid the user of a telephone accessory device. However the equipment typically provided by the telephone operating company is not only expensive and relatively complicated but it does not provide lamp and ringing control for use with a telephone accessory device.
It is therefore a further object of the instant invention to provide lamp and ringing control for any incoming line of a multi-line telephone system.